Striped sheaths for medical devices

ABSTRACT

A sheath used to protect a medical device has one or more strips formed over a portion thereof. The medical device is a scaffold crimped to a balloon and mounted to a catheter. The sheath is two-piece, including a protecting and constraining sheath part. The strips facilitate removal of the constraining sheath from the scaffold in manner that reduces instances of damage caused by improper removal of the sheath from the medical device.

FIELD OF THE INVENTION

The present invention relates to drug-eluting medical devices; moreparticularly, the invention relates to protective sheaths for scaffoldsand stents crimped to a delivery balloon.

BACKGROUND OF THE INVENTION

A variety of non-surgical interventional procedures have been developedover the years for opening stenosed or occluded blood vessels in apatient caused by the buildup of plaque or other substances in the wallsof the blood vessel. Such procedures usually involve the percutaneousintroduction of an interventional device into the lumen of the artery.In one procedure the stenosis can be treated by placing an expandableinterventional device such as an expandable stent into the stenosedregion to expand and hold open the segment of blood vessel or otherarterial lumen. Metal or metal alloy stents have been found useful inthe treatment or repair of blood vessels after a stenosis has beencompressed by percutaneous transluminal coronary angioplasty (PTCA),percutaneous transluminal angioplasty (PTA) or removal by other means.Metal stents are typically delivered in a compressed condition to thetarget site, then deployed at the target into an expanded condition ordeployed state to support the vessel.

The following terminology is used. When reference is made to a “stent”,this term will refer to a permanent structure, usually comprised of ametal or metal alloy, generally speaking, while a scaffold will refer toa structure comprising a bioresorbable polymer and capable of radiallysupporting a vessel for a limited period of time, e.g., 3, 6 or 12months following implantation. It is understood, however, that the artsometimes uses the term “stent” when referring to either type ofstructure. The disclosure herein applies to both stents and scaffolds.

Scaffolds and stents traditionally fall into two generalcategories—balloon expanded and self-expanding. The later type expandsto a deployed or expanded state within a vessel when a radial restraintis removed, while the former relies on an externally-applied force toconfigure it from a crimped or stowed state to the deployed or expandedstate.

Self-expanding stents are designed to expand significantly when a radialrestraint is removed such that a balloon is often not needed to deploythe stent. However, self-expanding stents do not undergo, or undergorelatively no plastic or inelastic deformation when stowed in a sheathor placed on a balloon. Balloon expanded stents or scaffolds, bycontrast, undergo a significant plastic or inelastic deformation whenboth crimped and later deployed by a balloon.

Self-expanding stents use sheaths to maintain a low profile and retainthe stent on a delivery catheter. Once at the target site, the sheath isthen removed or withdrawn in a controlled manner to facilitatedeployment or placement at the desired site. Examples of self-expandingstents constrained within a sheath when delivered to a target sitewithin a body are found in U.S. Pat. No. 6,254,609, US 20030004561 andUS 20020052640. Balloon expanded stents may also be stored within asheath, either during a transluminal delivery to a target site or duringthe assembly or in the packaging of the stent-balloon catheter deliverysystem. The balloon expanded stent may be contained within a sheath whendelivered to a target site to minimize dislodgment of the stent from theballoon while en route to the target vessel. Sheaths may also be used toprotect a drug eluting stent during a crimping process, which presses orcrimps the stent to the balloon catheter. When an iris-type crimpingmechanism, for example, is used to crimp a stent to balloon, the bladesof the crimper, often hardened metal, can form gouges in a drug-polymercoating or even strip off coating through interaction similar to forcesat play when the blades and/or stent struts are misaligned during thediameter reduction. Examples of stents that utilize a sheath to protectthe stent during a crimping process are found in U.S. Pat. No. 6,783,542and U.S. Pat. No. 6,805,703.

A polymer scaffold, such as that described in US 20100004735 may be madefrom a biodegradable, bioabsorbable, bioresorbable, or bioerodablepolymer. The terms biodegradable, bioabsorbable, bioresorbable,biosoluble or bioerodable refer to the property of a material or stentto degrade, absorb, resorb, or erode away after the scaffold has beenimplanted at the target vessel. Polymer scaffolds described in US2010/0004735 and US20110190872, as opposed to a metal stent, areintended to remain in the body for only a limited period of time. Inmany treatment applications, the presence of a stent in a body may benecessary for a limited period of time until its intended function of,for example, maintaining vascular patency and/or drug delivery isaccomplished. Polymeric materials considered for use as a polymericscaffold include poly(L-lactide) (“PLLA”), poly(L-lactide-co-glycolide)(“PLGA”), poly(D-lactide-co-glycolide) or poly(L-lactide-co-D-lactide)(“PLLA-co-PDLA”) with less than 10% D-lactide, and PLLD/PDLA stereocomplex.

When using a polymer scaffold, several of the accepted processes formetal stent handling can no longer be used. A metal stent may be crimpedto a balloon in such a manner as to minimize, if not eliminate recoil inthe metal structure after removal from the crimp head. Metal materialsused for stents are generally capable of being worked more during thecrimping process than polymer materials. This desirable property of themetal can mean less concern over the metal stent—balloon engagementchanging over time when the stent-catheter is packaged and awaiting usein a medical procedure. Due to the material's ability to be workedduring the crimping process, e.g., successively crimped and released athigh temperatures within the crimp mechanism, any propensity for elasticrecoil in the material following crimping can be significantly reduced,if not eliminated, without affecting the stent's radial strength whenlater expanded by the balloon. As such, following a crimping process thestent-catheter assembly often does not need packaging or treatment tomaintain the desired stent-balloon engagement and delivery profile. Ifthe stent were to recoil to a larger diameter, meaning elasticallyexpand to a larger diameter after the crimping forces are withdrawn,then significant dislodgment force could be lost and the stent-balloonprofile not maintained at the desired diameter needed to deliver thestent to the target site. Consequently, sheaths for metallic stents areoften solely protective, preventing contamination or mechanical damageto the stent and coating. They do not need to be closely fitted toprevent stent recoil on aging and storage.

While a polymer scaffold may be formed so that it is capable of beingcrimped in such a manner as to reduce inherent elastic recoil tendenciesin the material when crimped, e.g., by maintaining crimping blades onthe scaffold surface for an appreciable dwell period, the effectivenessof these methods are limited. Significantly, relatively high stiffnessand brittle polymer material is generally incapable of being worked tothe degree that a metal stent may be worked without introducing deployedstrength problems, such as excessive cracking in the material.

U.S. Pat. No. 8,414,528 proposes a two-piece sheath intended for removalby a medical professional at the time of the medical procedure. Thesheaths are placed over the crimped polymer scaffold shortly aftercrimping, for purposes of reducing or limiting the amount of recoil upuntil the time of use. The sheaths are designed to apply a radialconstraint for limiting recoil while, at the same time, allowing amedical professional to easily remove the sheath without damaging thecatheter or scaffold.

There is a need to improve upon sheaths used to protect medical deviceseither during processing, manufacture or, in the case of U.S. Pat. No.8,414,528, to protect the medical device while it awaits use and/or tofacilitate easy removal by a medical professional.

SUMMARY OF THE INVENTION

The invention is directed to sheaths and sheath assemblies used withmedical devices, including sheaths used to maintain a polymer scaffoldballoon engagement.

According to one aspect, a sheath used to protect a scaffold is madefrom a hollow, cylindrical polymer tube having a nominal diameter. Thetube is cut so that the tube can be manually withdrawn from a medicaldevice by a health professional without risk of damage to the medicaldevice, e.g., a scaffold. This cut sheath has, in some embodiments, acut length equal to about one half of the entire length of the sheath,or at least about the entire length of the scaffold.

Sheaths according to the invention are particularly useful formaintaining a scaffold-balloon engagement and desired delivery profilefollowing a crimping process where the scaffold is crimped down toachieve a smaller crossing-profile. A scaffold formed at a largerdiameter, near to or greater than the expanded or post-dilationdiameter, can exhibit enhanced radial strength when supporting a vessel,as compared to a scaffold formed nearer to a crimped diameter. Ascaffold formed near to an expanded or post-dilation diameter, however,increases the propensity for elastic recoil in the scaffold followingthe crimping process, due to the shape memory in the material. The shapememory relied on for enhancing radial strength at deployment, therefore,also introduces greater elastic recoil tendencies for the crimpedscaffold. Recoil both increases the crossing profile and reduces thescaffold-balloon engagement needed to hold the scaffold on the balloon.In one aspect, the invention is directed to maintaining the crossingprofile and/or maintaining balloon-scaffold engagement for scaffoldsformed near to a deployed diameter.

In another aspect, the invention is directed to a method of assembly ofa catheter that includes crimping a polymer scaffold to a balloon of thecatheter and within a short period of removal of the scaffold from thecrimper placing a restraining sheath over the scaffold. The steps mayfurther include applying an extended dwell time following a finalcrimping of the scaffold, followed by applying the restraining sheath.Both the crimping dwell time and applied restraining sheath are intendedto reduce recoil in the crimped scaffold. The restraining sheath mayinclude both a protecting sheath and a constraining sheath.

In another aspect, the invention is directed to a sterilized medicaldevice, e.g., by E-beam radiation, contained within a sterile package,the package containing a scaffold crimped to a balloon catheter and asheath disposed over the crimped scaffold to minimize recoil of thecrimped scaffold. The sheath covers the crimped scaffold and may extendbeyond the distal end of the catheter to facilitate removal from thescaffold. The sheath may extend at least the length of the scaffoldbeyond the distal end of the catheter. At the distal end of the sheaththere is a portion configured for being manually grabbed and pulled (orpushed) distally of the catheter to remove the sheath from the catheter.

In another aspect, the invention is directed to an apparatus and methodsfor removing a sheath pair from a scaffold in a safe, intuitive mannerby a health professional. According to this aspect of the invention, thesheath pair may be removed by a medical specialist such as a doctorwithout risk of the scaffold becoming dislodged from the balloon ordamaged, such as when the sheath pair is accidentally removed in animproper manner by a health professional.

In accordance with the foregoing disclosure and included within thescope of the invention, there is a scaffold and sheath(s), medicaldevice, method for making and/or assembling such a medical device,scaffold and/or sheath, a method for removal of sheaths form a medicaldevice, and method for making and/or assembly of a medical device (suchas a scaffold-balloon catheter assembly) comprising such a scaffoldand/or sheath having one or more, or any combination of the followingthings (1)-(32):

-   -   (1) A sheath including a constraining sheath and protecting        sheath. The constraining sheath has at least one slot.    -   (2) The constraining and protecting sheaths each have at least        one slot.    -   (3) More than 50% of the protecting sheath slot is beneath a        constraining portion of the constraining sheath and more than        50%, or 100% of the constraining sheath slot is not over the        protecting sheath slot when the constraining and protecting        sheaths are disposed over the scaffold.    -   (4) The protecting sheath has two slits or forms two halves and        the constraining sheath has at least one strip.    -   (5) A two piece sheath assembly disposed over a scaffold.    -   (6) An apparatus comprising sheaths disposed over and protecting        a scaffold, the apparatus consisting of only two sheaths: a        constraining sheath and a protecting sheath.    -   (7) The constraining sheath has two or three portions. When it        has three portions there is a first portion which includes the        sheath distal end, a second portion having at least one slot        extending over the entire length of the second portion, and a        third portion that includes the proximal end. When it has two        portions the sheath has only the second and third portions. The        second portion includes the distal end.    -   (8) There may be 2, 3, 4, 5, 6, 7, 8, 9 or 10 slots made.        Between two slots there is at least one strip. Depending on the        number of slots formed, a strip may span a circumferential angle        of about 10, 20, 30, 45, 60, 90, 120, 150, 180, 170, 10-50,        50-80, 90-130, 190-200, or 180-270 degrees.    -   (9) A slot may be narrow or wide. A narrow slot can be made by        cutting the sheath. A wide slot can be made by cutting twice        then removing sheath material between the cuts to form a slot        having a width equal to the distance between the two cuts.    -   (10) A slot is about straight and parallel to the sheath        longitudinal axis    -   (11) The slot is helical with a helix angle up to about 60        degrees. The helical slot forms a helix strip.    -   (12) The protecting sheath has a length about the same or larger        than the length of the constraining sheath. Ends of the        protecting sheath can have an outer diameter larger than the        outer diameter of the constraining sheath.    -   (13) One or both of a second and third portion, e.g., portions        34 and 36 of FIG. 1D, of the constraining sheath is greater than        or about equal to the length of the balloon/scaffold.    -   (14) The second and third portion lengths, e.g., lengths L34 and        L36, are based on a length of a scaffold. The lengths may be        about or at least the length of a scaffold, so that the        constraining sheath length is about twice the length of the        scaffold. Scaffold lengths for coronary use may be about 12 mm,        18 mm, 20 mm or 30 mm. The second and/or third portion lengths        may therefore be about or at least 12 mm, 18 mm, 20 mm or 30 mm        or be about or at least 12-20 mm, or be about or at least 12-18        mm or be about or at least 20-30 mm. Scaffold lengths for        peripheral use may be about 30 mm, 40 mm, 50 mm, 60 mm, 100 mm,        or 200 mm. The second and/or third portion lengths may therefore        be about or at least 30 mm, 40 mm, 50 mm, 60 mm, 100 mm, or 200        mm or be about or at least 30-60 mm, or be about or at least 100        to 200 mm or be about or at least 60-150 mm.    -   (15) The second portion may include the distal end of the        constraining sheath. In this case strips of the second portion        can freely pass over the end of the protecting sheath when the        constraining sheath is pulled or pushed off the scaffold. When        the second portion does not include the distal end of the sheath        then the strips fold up when the sheath is pushed or pulled off        the scaffold (compare e.g. FIGS. 1A, 1B with 2A).    -   (16) Before the sheaths are placed, the scaffold is crimped to        the balloon using a crimping mechanism. For a polymer scaffold        the diameter reduction during crimping may be 2:1, 2.5:1, 3:1,        4:1 or higher. The scaffold may be placed on a balloon having a        nominal, expanded or post-dilation diameter that is about 2,        2.5, or 3 times the diameter of the scaffold when the scaffold        has a final crimp diameter on the balloon.    -   (17) The sheath removal process as described with reference to        with FIGS. 1A and 1B or FIG. 2A.    -   (18) An inelastic crimping process at or near to a glass        transition temperature of the polymer of the scaffold conducted        in the manner explained in U.S. application Ser. No. 13/644,347        including FIGS. 3A and 4A.    -   (19) Ratio of crimped diameter to balloon nominal inflation        diameter or expanded diameter is greater than about 2, 2.5 or        greater than about 3 or 4; and/or the ratio of pre-crimp        diameter to balloon nominal diameter is about 0.9 to 1.5.    -   (20) The catheter and scaffold are configured as a medical        device suitable for being implanted within a body only after a        sheath(s) is/are removed. The catheter is not configured or        suitable for implantation when the sheath pair is over the        scaffold; or is implanted in use only after the sheath pair are        removed by pulling the sheath pair distally from the catheter to        remove the sheath pair from the catheter. The pulling may        include gripping an outer or constraining sheath and pulling it        distally (while the catheter is held stationary) so as to cause        removal of both the outer or constraining sheath and inner or        protecting sheath.    -   (21) A sheath, when protecting a crimped scaffold, has a        constraining sheath covering at least the entire length of the        scaffold and balloon and may extend beyond a distal tip of the        catheter by at least a scaffold length, ½ a scaffold length or ¼        of a scaffold length, and/or the distal end of a protecting        sheath.    -   (22) A protecting sheath has one or two flared, stepped or        notched ends, or no stepped or notched ends.    -   (23) A constraining sheath length that is less, about equal to,        or greater than a protecting sheath length.    -   (24) Slots are made sufficiently long so that the sheath can be        folded up to clear a constraining portion from the scaffold        during removal (e.g., FIG. 1B), while maintaining a distal end        of the constraining sheath as a cylindrical portion devoid of        slots.    -   (25) The protecting and/or constraining sheath may comprise        PTFE, PVDF, fluoropolymer, polyethylene, polypropylene, nylon,        nylon copolymers, Pebax, polyacetal, or polyimide.    -   (26) The polymer comprising the scaffold is bioresorbable, or        the stent comprises a durable, non-bioresorbable, or        non-bioerodible polymer.    -   (27) A method for maintaining a low crossing profile and/or        retention for a polymer includes crimping a scaffold to a        balloon, placing a first sheath over the crimped scaffold; and        replacing the first sheath with a second sheath.    -   (28) An apparatus comprising a catheter having distal and        proximal ends; a scaffold crimped to a balloon at the catheter        distal end; and a two piece sheath assembly, including a        protecting sheath disposed over the scaffold, a constraining        sheath disposed over the protecting sheath, and the constraining        sheath including at least one strip; wherein the crimped        scaffold and balloon are configured for being placed within a        body only after the two piece sheath assembly is pushed or        pulled off the catheter distal end.    -   (29) The apparatus of (28) and (32) or method of (30), in        combination with one of, more than one of, or any combination in        any order of the following list of things: wherein the        protecting sheath includes two slots; wherein the two slots form        separable halves; wherein the constraining sheath has a second        and third portion each having lengths L2 and L3 and the scaffold        has a length LS, wherein L2 and/or L3 is about equal to LS;        wherein the sum L2+L3 is about twice LS; wherein the scaffold        has a distal end and a proximal end, and wherein a substantial        portion of the at least one strip is disposed distally of the        scaffold distal end and/or the catheter distal end; wherein more        than 50% of a lengthwise extent of the at least one strip is        located distally of the catheter distal end; wherein the        constraining sheath comprises a plurality of slots, wherein the        at least one strip is formed between a pair of slots; wherein        the constraining sheath has a constraining portion devoid of a        strip, and the constraining portion is disposed over the entire        length of the scaffold; wherein the protecting sheath includes        at least two slots, and the constraining portion is disposed        over the two slots and the scaffold; wherein the at least one        strip extends parallel to a longitudinal axis of the catheter;        wherein the strip is a helical strip formed by a single helical        slot having a helix angle; wherein a distal end of the        constraining sheath comprises a portion of the at least one slot        and strip; wherein the constraining sheath includes six slots        and six strips, four slots and four strips, or two slots and two        strips; and/or wherein the constraining sheath slot is located        distally of a distal end of the scaffold and a constraining        portion of the constraining sheath applies an inwardly directed        radial pressure upon the scaffold to reduce recoil of the        scaffold.    -   (30) A method of removing a sheath from a scaffold mounted on a        catheter having a distal end, the sheath including a        constraining sheath and protecting sheath disposed over the        scaffold, comprising: pushing or pulling the constraining sheath        over the protecting sheath and distally of the catheter distal        end, including a portion of the constraining sheath located        distal of the catheter distal end sliding over the protecting        sheath, and a distal end of the constraining sheath abutting a        distal end of the protecting sheath and causing a strip of the        constraining sheath to deflect away from the protecting sheath.    -   (31) The apparatus of (28) and (32), method of (30) or        additional features of invention in (29), in combination with        one of, more than one of, or any combination in any order of the        following list of things: wherein the deflected strip slides        over the protecting sheath distal end; and/or wherein the        deflected strip folds up at a location proximal of the        protecting sheath distal end.    -   (32) An apparatus, comprising: a catheter including a scaffold        crimped to a balloon; and a sheath assembly including a        protecting sheath disposed over the scaffold, a constraining        sheath disposed over the protecting sheath, a constraining        sheath slot not disposed over the scaffold, and a protecting        sheath slot disposed over the scaffold.

INCORPORATION BY REFERENCE

All publications and patent applications cited and discussed in thepresent specification are herein incorporated by reference in theirentirety, to the same extent as if each individual publication or patentapplication was specifically and individually indicated to beincorporated by reference in its entirety, including all figures,herein. To the extent there is an inconsistent usage of a word and/orphrase between an incorporated publication or patent application and thepresent specification, this word and/or phrase will have a meaningconsistent with only the manner that the word and/or phrase is used inthe present specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is side view of a medical device and sheath according to thedisclosure.

FIG. 1A is a side view of the medical device and sheath of FIG. 1 with aconstraining sheath partially withdrawn towards a distal end of thesheath.

FIG. 1B is a side view of the medical device and sheath of FIG. 1A withthe constraining sheath fully withdrawn and an inner protecting sheathopening.

FIGS. 1C and 1D are front cross-sectional and side views, respectively,of the constraining sheath of FIG. 1. FIG. 1D is a side view taken fromperspective ID-ID in FIG. 1C.

FIG. 2 is side view of the medical device of FIG. 1 and an alternativeembodiment of a sheath according to the disclosure.

FIG. 2A is a side view of the medical device and sheath of FIG. 2 with aconstraining sheath fully withdrawn and an inner protecting sheathopening.

FIGS. 2B and 2C are front cross-sectional and side views, respectively,of the constraining sheath of FIG. 2. FIG. 2C is a side view taken fromperspective IIC-IIC in FIG. 2B.

FIG. 3 is a front cross-sectional view showing an alternative embodimentof a constraining sheath.

FIGS. 4A, 4B and 4C are perspective and side views, respectively, of aprotecting sheath according to the disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

For purposes of this disclosure, the following terms and definitionsapply:

The terms “about” or “approximately” mean 30%, 20%, 15%, 10%, 5%, 4%,3%, 2%, 1.5%, 1%, between 1-2%, 1-3%, 1-5%, or 0.5%-5% less or morethan, less than, or more than a stated value, a range or each endpointof a stated range, or a one-sigma, two-sigma, three-sigma variation froma stated mean or expected value (Gaussian distribution). For example, d1about d2 means d1 is 30%, 20%, 15%, 10%, 5%, 4%, 3%, 2%, 1.5%, 1%, orbetween 1-2%, 1-3%, 1-5%, or 0.5%-5% different from d2. If d1 is a meanvalue, then d2 is about d1 means d2 is within a one-sigma, two-sigma, orthree-sigma variation from d1.

It is understood that any numerical value, range, or either rangeendpoint (including, e.g., “approximately none”, “about none”, “aboutall”, etc.) preceded by the word “about,” “substantially” or“approximately” in this disclosure also describes or discloses the samenumerical value, range, or either range endpoint not preceded by theword “about,” “substantially” or “approximately.”

U.S. application Ser. No. 13/924,421 filed Jun. 21, 2013 (the '421application) includes a discussion about the meaning of terms such as“rigid,” “Inflated diameter” or “expanded diameter,” “post-dilationdiameter,” “pre-crimp diameter,” “final crimped diameter,” “recoil,”“acute recoil,” “radial,” “circumferential,” “axial” and “longitudinal.”

A “crimping” or “inelastic crimping” of a stent or scaffold means,unless otherwise stated, a significant plastic or inelastic deformationof the stent or scaffold (body), such that when a radial restraint isremoved from the crimped body, e.g., a constraining sheath is withdrawn,the scaffold or stent will change diameter (due to elastic recoil) by nomore than about 5%, 10%, 20%, 30% or 50% increase from the crimpeddiameter. A body crimped to the balloon is held to the balloon by aretention force. A crimped body is deployed within the body by a balloonthat imposes a significant inelastic or plastic deformation to expandthe body to a deployed expanded or post-dilation diameter. The crimpedbody when deployed also has elastic recoil causing it to reduce indiameter by about 1, 2, 1-5%, 5-10% or 10%.

A structure X “configured for being implanted within a living body”means X is placed within a living body in use or X is capable of beingplaced within the body, e.g., delivered intraluminally through thevasculature of a living body. A structure Y not suited, capable orconfigured for being placed within a living body means if placed withinthe living body in a proscribed manner would pose serious health risksto the living body. A structure Z “configured for implantation onlyafter . . . ” means Z is placed within a living body in use or X iscapable of being placed within the living body and deliveredintraluminally through the vasculature of a living body only after aspecific step is undertaken to convert Z to X. Thus, for example, anapparatus comprising a catheter, a scaffold mounted on a balloon and atwo-piece sheath on the scaffold “configured for implantation in aliving body only after . . . ” the two-piece sheath is pulled distallyto remove it from the scaffold (Z) means (Z) is converted to X onlyafter “the two-piece sheath is pulled distally to remove it from thescaffold.” In this example, a tearing, ripping or destruction of thesheath when removing it does not convert Z to X because the sheath wasnot pulled distally of the catheter to remove it from the catheter.Moreover, it will be understood, referring to preferred embodiments asexamples, that when a two-piece sheath according to the disclosure ispositioned over a scaffold there is no way available for the sheaths tobe removed using the catheter proximal end handle.

The following description is directed to preferred embodiments of apolymer scaffold crimped to a balloon of a balloon catheter andprotected by a protective sheath. The apparatus is configured forimplantation within a living body only after the sheath is pushed orpulled off the catheter distal end. This sheath includes a constrainingor outer sheath manufactured according to the above process.

A polymer scaffold is formed from a radially expanded or biaxiallyexpanded extruded PLLA tube. The degree of radial expansion (RE) andaxial expansion (AE) that the polymer tube undergoes can characterizethe degree of induced circumferential molecular and crystal orientationas well as strength in a circumferential direction. In some embodimentsthe RE is about 400% and the AE is 40-50%. Other embodiments ofprocessing parameters, RE and AE expansions considered within the scopeof the disclosure are found in U.S. application Ser. No. 13/840,257filed Mar. 15, 2013. The scaffold is laser cut from the expanded tube.The diameter of the tube is preferably selected to be about the same, orlarger than the intended deployed diameter for the scaffold to provideddesirable radial strength characteristics, as explained earlier. Thescaffold is then crimped onto the balloon of the balloon catheter.Preferably, an iris-type crimping mechanism is used to crimp thescaffold to the balloon. The desired crimped profile for the scaffold is½ or less than ½ of the starting (pre crimp) diameter of the expandedtube and scaffold. In the embodiments, the ratio of the startingdiameter or pre-crimp diameter to the final crimp diameter may be 2:1,2.5:1, 3:1, or higher and the pre-crimp diameter may be about 0.9 toabout 1.5 higher than the balloon nominal inflation diameter. The ratioof pre-crimp or intermediate crimp diameter to final crimped diametermay be greater than a ratio of expanded or post-dilation diameter to thefinal crimped diameter of the scaffold.

The pre-crimp memory in the scaffold material following crimping willinduce some recoil when the scaffold is removed from the crimper. Whilea dwell period within the crimper can reduce this recoil tendency, thereis residual recoil to restrain while the scaffold awaits use. This isdone by placing a restraining sheath over the scaffold after the crimperblades are released and the scaffold removed from the crimper head. Thisneed to reduce recoil is particularly evident when the diameterreduction during crimping is high, e.g., as in above examples, since fora larger starting diameter compared to the crimped diameter the crimpedmaterial can have higher recoil tendencies. Examples of polymers thatmay be used to construct sheaths described herein are Pebax, PTFE,polyethylene, polycarbonate, polyimide and nylon. Examples ofrestraining sheaths for polymer scaffolds and methods for attaching andremoving restraining sheaths for polymer scaffolds are described inUS20120109281, US20120324696 and U.S. Pat. No. 8,414,528, and U.S.application Ser. No. 13/708,638.

FIG. 1 shows a side view of a distal portion of a scaffold-ballooncatheter assembly 2. The catheter assembly 2 includes a catheter shaft 4and a scaffold 10 crimped to a delivery balloon 12. As shown there aretwo separate sheaths 20, 30 disposed over the scaffold 10. The scaffold10 is contained within a protecting sheath 20 and a constraining sheath30, which is slid over the outer surface of the protecting sheath 20 toposition it over the scaffold 10. Before inserting the catheter assembly2 distal end within a patient, both the constraining sheath 30 andprotecting sheath 20 are removed by a health professional.

The sheaths 20, 30 may be configured to provide an effective radialconstraint for reducing recoil in the crimped scaffold 10, in additionto protecting the scaffold and balloon prior to use. The sheaths 20, 30are removed by a health professional at the time of a medical procedureby pulling or pushing the outer sheath 30 towards the distal end of thescaffold 10 and balloon 12. With regard to other known devices, theremoval of a single sheath covering a medical device can cause damage tothe medical device. As described herein, a sheath that applies a radialconstraint can be difficult to manually remove without adverselyaffecting the structural integrity of the medical device. In thesecases, it is desirable to arrange the sheaths so that special handlingis not required by the health professional when the sheath is manuallyremoved. By making the sheath removal process easy to follow orintuitive, the possibility that a health professional will damage themedical device by improperly removing the sheath is reduced.

It is understood that if there are excessive pulling forces on thescaffold 10 when sheaths are removed, the catheter shaft 4 may bedamaged, the scaffold 10 may dislodge from a balloon 12, or shift on theballoon 12; thereby reducing scaffold-balloon engagement relied on tohold the scaffold 10 to the balloon 12. Although imposing a tight fit onthe scaffold 10 (through sheath 20), sheath 30, however, can be safelyremoved by a health professional without risk of damaging the medicaldevice. Prior to removal of a sheath according to the disclosure, e.g.,sheaths illustrated in FIG. 1, 2, 3 or 4A-4C, it will be well understoodthat the medical device being protected by the sheath cannot be usedsince it cannot be placed within a living body. Sheaths according tosome aspects of the disclosure are configured for implantation in aliving body only after a sheath is pulled or pushed off a catheterdistal end. Such sheaths may not be configured for being implanted ifthe sheaths are removed by tearing or removing the sheath from themedical by another method. The medical device is configured for beingimplanted only if the sheath is pushed or pulled off the sheath so thatthe sheath is removed from an end distal of the medical device.

When the scaffold 10 is constrained by sheath 30, as in FIG. 1, theconstraining sheath 30 is located over the section of the protectingsheath 20 where the crimped scaffold 10 is found. This sheath 30 is madefrom a polymer tube material having a thickness and pre-stressed innerdiameter size suitably chosen to cause the sheath 30 to apply a radiallyinward directed force on the scaffold 10. The thicker the tube and thesmaller the pre-stressed inner diameter size for the sheath 30 thehigher this constraint will be on the scaffold 10. If only sheath 30were applied, i.e., the sheath 20 is not present, the amount of preloadthat the sheath 30 could apply to the scaffold 10 without affectingscaffold-balloon engagement would be limited. However, by introducingthe protecting sheath 20 between the scaffold-balloon surface and sheath30 the sheath 30 can impose a higher preload on the scaffold 10 withoutrisk to the integrity of the scaffold-balloon engagement when the sheath30 is applied to and/or removed from the scaffold 10. The protectingsheath 20 therefore serves to protect the integrity of thescaffold-balloon structure as the sheath 30 is repositioned relative tothe scaffold 10. An example of a one-piece sheath capable of performingin a similar manner is found in US2012/0324696 at FIGS. 5 and 6A-6D.Other sheaths within the scope of the embodiments, including sheaths incombination with delivery tubes or coils, are found in U.S. applicationSer. No. 13/924,421 filed Jun. 21, 2013.

The protecting sheath 20 extends over the entire length of the scaffold(as shown) and preferably beyond the distal tip of the catheter assembly2 (as can be seen in FIG. 1) may the sheath 20 extend. The protectingsheath 20 is preferably formed from a unitary piece of polymer material,which is shaped to form differently sized portions 21, 22, 24 and 25 forprotecting the scaffold/balloon 10/12. FIGS. 4A, 4B and 4C showperspective and side views, respectively, of sheath 20.

At the distal end 20 b of sheath 20 there is a raised end 22 in the formof a cylinder section having a larger diameter than the body portion 21of the sheath 20 to the right of end 22 which covers the scaffold 10 inFIG. 1. Raised end 22 provides an abutting surface with respect todistal movement of sheath 30, i.e., end 30 b of sheath 30 abuts end 22when sheath 30 is moved to the left in FIG. 1. End 22 and/or end 24 mayalternatively take the shape of a frusto-conical or fluted end with thelargest diameter end being furthest from portion 21. The raised end 22may function to remove the sheaths 20, 30 simultaneously, as explainedbelow.

Except as where noted herein, the protecting sheath 20 according to thedisclosure may be the same, except as noted herein, as the protectingsheath described in US2012/0324696, US20120109281, US20120324696 andU.S. Pat. No. 8,414,528, and U.S. application Ser. No. 13/708,638.

Referring to FIGS. 1, 4A, 4B and 4C, the protecting sheath 20 has a slot26 (e.g., a slit or cut), extending from the proximal end 20 a to alocation about at the distal the tip of the catheter assembly 2 (orsheath 20). The slot 26 forms an upper and lower separable halve 28, 29of the sheath 20 (FIG. 4C). These halves 29, 28 are configured to freelymove apart when the sheath 30 is positioned towards the distal end 20 b.The location 26 a may be thought of as a living hinge 26 a about whichthe upper half 29 and lower half 28 of the sheath 20 can rotate, ordeflect away from the scaffold 10. When sheath 30 is moved distally, orto the left of the scaffold 10 in FIG. 1, the halves 28, 29 will tend toopen up naturally, due to the preload applied by sheath 30 near hinge 26a. This arrangement for halves 29, 28 provides easy removal of sheath 20from the scaffold 10, with minimal disruption to scaffold-balloonstructural integrity, after sheath 30 is moved towards distal end 20 b.When sheath 30 is fitted over the scaffold 10 or removed from thescaffold 10, the presence of the halves 28, 29 prevent direct contactbetween the sliding sheath 30 and the surface of the scaffold 10.

Sheath 20 may alternatively be formed as two completely separablehalves, e.g., as halves 145 a and 140 a illustrated in FIG. 11C of US2012/0324696 or as one sheath as shown in FIG. 4B but with the slot 26running the length of, or substantially the entire length of the sheath20. In the case of the former sheath 20 embodiment, sheath 150 of FIG.11C of US2012/0324696 is replaced by the sheath 30 illustrated in FIG. 6or other suitable embodiments thereof.

Embodiments of proximal end 20 a of sheath 20 and methods of use arediscussed in previously cited sheath disclosures, e.g., FIG. 1A and theaccompanying discussion in U.S. Pat. No. 8,414,528. Referring to thisdisclosure and the foregoing, it is understood that scaffold-balloonintegrity may be protected by the presence of the halves 28, 29 and thenotched portion 25.

In some embodiments the sheath 20 may extend to about the end of thecatheter and preferably at least to the end of the catheter. In apreferred embodiment an extended length of sheath 20, beyond the tip ofthe catheter assembly 2, e.g., may be about equal to a length of thescaffold 10 and/or greater than this length. This length beyond thedistal tip may facilitate an intuitive sliding removal or attachment ofthe sheath 30 from/to the scaffold 10 by respectively sliding the sheath30 along the sheath 20 extension that is beyond the distal tip of thecatheter assembly 2. Or this extended length allows the sheaths 20, 30to be removed with the same pulling motion while the search 30 is notapplying a radial constraint on the scaffold. The length of the sheath20 that extends beyond the distal end of the catheter assembly 2 (lengthL21 in FIG. 4A of US2012/0324696) may depend on the choice of sheathsused. For example, from the perspective of the health professionalremoval process, if the sheath 20 is more stiff (e.g., higher wallthickness and/or modulus) relative to the sheath 30 then the lengthbeyond distal end 4 for sheath 20 may be longer so that the halves 28,29 of sheath 20 can be more safely displaced from the scaffold 10 byclearing the sheath 30 more distally of the scaffold 10. If the sheath30 wall thickness and/or modulus is higher relative to sheath 20 thanthe length may be shorter since the sheath 30 will tend to naturallyopen up the halves 28, 29 as it is moved distally of the distal tip ofthe catheter assembly 2. Also, a thicker or higher modulus sheath 20and/or sheath 30 may be desirable to increase the resistance to improperremoval of sheath 20, e.g., as when a user attempts to remove sheath 20with, or before removing sheath 30 from the scaffold 10 (as discussedearlier).

Referring to FIGS. 1, 1A, 1B, 1C and 1D a constraining sheath 30 has adistal end 30 b and proximal end 30 a. The length of the sheath 30 fromproximal end 30 a to distal end 30 b is L30. The sheath 30 may bedescribed as having three portions; namely, a first portion 32 whichincludes the distal end 30 b, a second portion 34 having at least oneslot 38 extending over the entire length L34 of second portion 34, andthird portion 36 which includes the proximal end 30 a. The lengths ofportions 32, 34 and 36 are respectively L32, L34 and L36 andL30=L32+L34+L36. In a preferred embodiment a unitary tube of constantdiameter throughout is made into the sheath 30 having the portions 32,34 and 36. Examples of polymers for sheath 30 include Pebax, PTFE,polyethylene, polycarbonate, polyimide and nylon.

The portion 34 is preferably, but need not be formed by cutting the tubeto form one slot 38, or more than one slot 38. According to thedisclosure there may be 2, 3, 4, 5, 6, 7, 8, 9 or 10 slots in sheath 30.Between two slots 38 there is at least one strip 37. When there are 10slots there are 5 strips. When there are two slots there is at least onestrip (FIG. 2A). In FIG. 1D there is shown a strip 37 between slots 38 aand 38 b. Depending on the number of slots formed, a strip may span acircumferential angle of about 10, 20, 30, 45, 60, 90, 120, 150, 180,170, 10-50, 50-80, 90-130, 190-200, or 180-270 degrees. In theillustrated embodiment of FIGS. 1A, 1B, 1C and 1D there are 6 evenlyspaced slots forming three strips 37 a, 37 b, 37 c, 37 d, 37 e and 37 f.Each strip 37 spans an angle of about π/3 radians (θ=π/3). FIG. 3showing an alternative embodiment of portion 34 has four evenly spacedstrips 237 a, 237 b, 237 c and 237 b each spanning an angle of about π/4radians (θ=π/4). There are four slots 238.

A slot 38 may be narrow or wide. For example, when a slot is formed bycutting there is essentially no, or a narrow opening between theadjacent edges until the sheath 30 is deformed as in FIGS. 1A and 1B. Aslot 38 may have a wide opening, e.g., by cutting slits then removingthe sheath material between the slits. For example, the strip 37 in FIG.1D if removed would form a slot having a width about the same as thewidth of the strip 37 removed. Embodiments of sheath 30 contemplatedfurther include 1 or 2 wide slots, or a plurality of slots all havingabout the same, or different widths. In one embodiment at least one slothas a length equal L34 and at least one slot that has a length less thanL32 or the length of the other slot.

Another embodiment has a single, helical slot extending over the lengthL34 as opposed to one or more horizontal or longitudinal slots. Thehelix angle, i.e., the angle with respect to horizontal or longitudinaldirection in FIG. 1D, may be about 10, 20, 40, or up to 60 degrees. Ahelix strip is formed by the helical slot. The helix strip may be formedby cutting a helical slit over the length L34 of portion 34.

The slots 38 do not extend into portion 32. Instead, portion 32 has anintact cylindrical shape (free of slots) as in the case of portion 36.The length L32 may be such that the sum L34+L36 is equal to about 70,80, 90 or 85% of L30 or (L34+L36) is slightly less than L30. Theportions 32 and 34 may be made by cutting from the end of portion 36through to the distal end 30 b then re-connecting the cuts over portion32. Or the portions 32 and 34 may be formed by making cuts from the endof portion 36 up until portion 32; or slots are made sufficiently longso that the sheath 30 can be folded up to clear portion 36 from thescaffold, as shown in FIG. 1B, while maintaining the end 30 b as acylindrical portion devoid of slots.

Referring to FIGS. 1, 1D and FIGS. 4A-4C protecting sheath 20 has thelength L20. The length L30 may be about or slightly less than L20. L20may be longer than L30 by an amount about equal to the length of raisedend 22 or ends 22 and 24. The outer diameter of sheath 30 may be lessthan the outer diameter of end 22 so that end 22 acts as a stop forsheath 30 when sheath 30 is pulled distally during removal from thecatheter (FIGS. 1A-1B). L36 is greater than or about equal to the lengthof the balloon/scaffold 10/12. L34 may be greater than, or about equalto or less than the length of the balloon/scaffold 10/12.

The lengths L36 and/or L34 may be based on a length of a scaffold. Forexample, both L34 and L36 may be about or at least the length of ascaffold, so that the L30 is about twice the length of the scaffold.Scaffold lengths for coronary use may be about 12 mm, 18 mm, 20 mm or 30mm. The lengths L34 and/or L36 may therefore be about or at least 12 mm,18 mm, 20 mm or 30 mm or be about or at least 12-20 mm, or be about orat least 12-18 mm or be about or at least 20-30 mm. Scaffold lengths forperipheral use may be about 30 mm, 40 mm, 50 mm, 60 mm, 100 mm, or 200mm. The lengths L34 and/or L36 may therefore be about or at least 30 mm,40 mm, 50 mm, 60 mm, 100 mm, or 200 mm or be about or at least 30-60 mm,or be about or at least 100 to 200 mm or be about or at least 60-150 mm.

Referring to FIGS. 2, 2A, and 2B, the medical device is shown with analternative embodiment of a sheath. Specifically, there is shown theinner protecting sheath 20 (as before) with an alternative outerconstraining sheath 130 according to the disclosure. Where the sameelement numbers are used in the following discussion the samedescription as before applies.

For the alternative embodiment, instead of having three portions 32, 34and 36 there are only two portions 134 and 136 for sheath 130. Theportion 134 includes the distal end 30 b. The lengths L30, L34 and L36described earlier in respect to the lengths of portions 32, 30 and 36apply equally to the lengths for portions 134 and 136, i.e., lengthsL134 and L136 except as follows. The length L130 is always equal to thesum of L134+L136 because there is no portion having distal end 30 b andbeing devoid of slots. Other than this change, all discussion concerningthe shape, width, number, angles and arrangement and locations of slots38 and strips 37 apply equally to the strips 137 and slots 138 shown inFIGS. 2, 2A, and 2B.

The illustrated sheath 130 has two slots 138 circumferentially spaced byabout π/2 radians. The two strips 137 a and 137 b formed there betweenalso span an angle of about π/2 radians. One difference between thesheath 130 and the sheath 30 is that the strips 137 freely deflect awayfrom the end 22 of the sheath 20 when the proximal end 30 a is pulled orpushed toward end 22, as illustrated in FIG. 2A. The strips 37 of sheath30 fold up when the proximal end 30 a is pulled or pushed toward end 22,as illustrated in FIGS. 1A and 1B.

Methods of assembly of a medical device according to some aspects of thedisclosure are now described. The medical device in its assembled stateincludes the scaffold crimped to a balloon catheter and the two piecesheath disposed over the scaffold as in FIG. 1. The catheter assembly 2with sheaths arranged as in FIG. 1 may be contained within a protectingtube, hermetically sealed and sterilized. At the time when the catheterassembly is to be used in a medical procedure the package is opened andthe tube and sheath pair is removed before implantation.

Before the sheaths 20/30 or 20/130 are placed, the scaffold 10 iscrimped to the balloon 12 of the catheter assembly 2 using a crimpingmechanism. As noted above, for a polymer scaffold the diameter reductionduring crimping may be 2:1, 2.5:1, 3:1, 4:1 or higher. The scaffold maybe placed on a balloon having a nominal, expanded or post-dilationdiameter that is about 2, 2.5, or 3 times the diameter of the scaffoldwhen the scaffold has a final crimp diameter on the balloon. Thediameter reduction (from a pre-crimp size to the final crimp diameter)introduces high stresses in the scaffold structure. The memory in thematerial following crimping causes recoil of the scaffold structure, asdiscussed earlier; one can incorporate lengthy dwell times within thecrimper, e.g., after the final crimp step, to allow stress-relaxation tooccur in the structure while heated crimper blades are maintaining afixed diameter and temperature to facilitate stress relaxation. Both thedwell period and the imposition of a constraining sheath over thecrimped scaffold after crimping helps to reduce recoil after crimping.Crimping of the scaffold 10 to the balloon 12 including desirable dwelltimes and temperatures that can affect stress relaxation and recoilafter crimping are disclosed in U.S. patent application Ser. No.12/861,719, U.S. patent application Ser. No. 13/089,225 and U.S. patentapplication Ser. No. 13/107,666.

Following removal from a crimping mechanism the scaffold will recoilunless subject to a radial constraint. According to some aspects of thedisclosure a temporary one-piece sheath is placed on the scaffoldimmediately following crimping, then replaced by the sheath of FIG. 6after about ½ hour from removal from the crimping mechanism. Examples ofthe one-piece sheath according to the disclosure is one-piece sheath 23described in U.S. application Ser. No. 13/708,638.

FIGS. 1A-1B illustrate a removal process for the sheath pair 20/30 by amedical professional. The assembly of the sheath pair 20/30 over theballoon/scaffold 12/10 (the assembly shown in FIG. 1) may be the same asthe assembly process described in US20120109281, US20120324696 and U.S.Pat. No. 8,414,528, and/or U.S. application Ser. No. 13/708,638.

A method of removal of the sheath 20/30 from the scaffold 10 is nowdescribed. At the time when the catheter assembly is to be used in amedical procedure the package is opened and the sheath pair is removedfrom the distal end. The catheter assembly 2 is not configured for beingintroduced into the patient until the sheath pair is removed. Referringagain to FIG. 1, there is depicted an arrangement of the sheaths 20, 30at the distal end of the catheter assembly 2 when the packaged andsterile medical device is received by a health professional. Examples ofsuch sterile packaging is found in U.S. patent publication no. US2008-0010947.

The sheath 20 may extend well-beyond the distal end of the catheter 2assembly. The end 22 may overhang or sit distal the catheter distal endby a full, half or ¼ the scaffold or length L30. The overhanging ordistal portion with portions 34 and 32 substantially covering the distalportion of sheath 20 (when received by the medical professional) helpsto facilitate an intuitive removal of the sheath pair by a healthprofessional, thereby reducing the chances that the sheath pair areremoved improperly, such as a removal by pulling on, or gripping thesheath 20 instead of the portion 36 or 34.

A sterilized and packaged catheter assembly with sheaths 20, 30positioned as shown in FIG. 1 typically includes the stiffening orstorage mandrel in the catheter shaft 4 lumen to provide bendingstiffness for shaft 4. A distal end of the mandrel (not shown) has acurled end, or an extension/stop at the distal end (not shown), which isused to manually withdraw the mandrel 8 from the catheter shaft 4 lumenby pulling the mandrel 8 towards the distal end of the catheter assembly2. In the following example the sheaths 20, 30 are removed. Theproscribed steps preferably also include the act of removing the mandrel8 from the catheter shaft lumen by, e.g., simultaneously gripping theraised end 22, sheath 30 and mandrel.

The sheath 30 is pinched or grabbed and pulled (or pushed) toward end 22and away from the scaffold-balloon 10/12 structure, which removes theconstraining portion 36 from the scaffold-balloon 10/12 structure. Thesheath 30 may be withdrawn or pulled away from the scaffold-balloon10/12 in the following manner. One hand grasps the sheath 30; the otherhand grasps the catheter shaft 4 proximal of the scaffold 10 to hold thecatheter 2 stationary. The sheath 30 is pulled towards end 22. The end30 b abuts the end 22.

Referring to FIGS. 1A and 1B, as the sheath portion 36 is pulled awayfrom the balloon scaffold 12/10 the strips 37 begin to fold up (theouter diameter of portion 32 is less than the outer diameter of end 22,so portion 32 does not slip over end 22 and move distally of end 22).The sheath portion 36 continues to be pulled back until the portion 36essentially no longer over the scaffold 10, or until the halves 29, 28begin to open. In some cases the user may simply grab the portion 36 andcontinue pulling distally (as shown) until both sheaths 20 and 30 areremoved from the catheter 2. One advantage of the sheath 30 is that thetwo sheaths remain together after being removed from the scaffold, or sothat the sheath 30 is less likely to be removed prematurely oraccidentally from the sheath 20.

FIG. 2A illustrates the removal process when sheath 130 is used insteadof sheath 30. Since there is no portion 32 the strips 137 may freelypass over the end 22. In the same manner as described for sheath 30, thesheath portion 136 continues to be pulled back until the portion 136essentially no longer over the scaffold 10, or until the halves 29, 28of sheath 20 begin to open. In some cases the user may simply grab theportion 136 and continue pulling distally (as shown) until both sheaths20 and 130 are removed from the catheter 2.

According to a method of crimping, a crimping process at or near to aglass transition temperature of the polymer of the scaffold 10 isconducted as explained in U.S. application Ser. No. 13/644,347 includingFIGS. 3A and 4A. Before placing a two-piece sheath as described above, atemporary sheath may be formed with slits or weakened areas that willfacilitate a tearing away of the sheath when it is attached to thescaffold. Examples of such a sheath is described in U.S. applicationSer. No. 13/708,638 as shown in FIGS. 2, 3A-3E and 4.

The above description of illustrated embodiments of the invention,including what is described in the Abstract, is not intended to beexhaustive or to limit the invention to the precise forms disclosed.While specific embodiments of, and examples for, the invention aredescribed herein for illustrative purposes, various modifications arepossible within the scope of the invention, as those skilled in therelevant art will recognize.

These modifications can be made to the invention in light of the abovedetailed description. The terms used in claims should not be construedto limit the invention to the specific embodiments disclosed in thespecification.

What is claimed is:
 1. An apparatus, comprising: a catheter havingdistal and proximal ends; a scaffold crimped to a balloon at thecatheter distal end; and a two piece sheath assembly, including aprotecting sheath disposed over the scaffold, and a constraining sheathdisposed over the protecting sheath, the constraining sheath comprisingat least one strip, a first portion not disposed over the scaffold, anda second portion disposed over the scaffold, wherein a length of thesecond portion is greater than a length of the scaffold, and a length ofthe first portion is greater than the length of the second portion; andwherein the crimped scaffold and balloon are configured for being placedwithin a body only after the two piece sheath assembly is pushed orpulled off the catheter distal end.
 2. The apparatus of claim 1, whereinthe protecting sheath includes two slots.
 3. The apparatus of claim 2,wherein the two slots form separable halves.
 4. The apparatus of claim3, wherein the separable halves are completely separable halves.
 5. Theapparatus of claim 1, wherein the at least one strip spans an angle ofabout π/2 radians.
 6. The apparatus of claim 1, wherein the scaffold hasa distal end and a proximal end, and wherein a substantial portion ofthe at least one strip is disposed distally of the scaffold distal end.7. The apparatus of claim 1, wherein more than 50% of a lengthwiseextent of the at least one strip is located distally of the catheterdistal end.
 8. The apparatus of claim 1, wherein the constraining sheathcomprises between 3 and 10 slots and the at least one strip is formedbetween a pair of the slots.
 9. The apparatus of claim 1, wherein theconstraining sheath has a constraining portion devoid of a strip, andthe constraining portion is disposed over the entire length of thescaffold.
 10. The apparatus of claim 9, wherein the protecting sheathincludes at least two slots, and the constraining portion is disposedover the two slots and the scaffold.
 11. The apparatus of claim 1,wherein the at least one strip extends parallel to a longitudinal axisof the catheter.
 12. The apparatus of claim 1, wherein there is onestrip that is a helical strip formed by a single helical slot having ahelix angle.
 13. The apparatus of claim 1, wherein a distal end of theconstraining sheath comprises two slot portions and a portion of the atleast one strip, wherein the strip is between the two slot portions. 14.The apparatus of claim 1, wherein the constraining sheath includes sixslots and six strips, four slots and four strips, or two slots and twostrips.
 15. An apparatus, comprising: a catheter including a scaffoldcrimped to a balloon; and a sheath assembly including a protectingsheath disposed over the scaffold, a constraining sheath disposed overthe protecting sheath, a constraining sheath slot not disposed over thescaffold, and a protecting sheath slot disposed over the scaffold;wherein the constraining sheath comprises a first portion not disposedover the scaffold and a second portion disposed over the scaffold, andwherein a length of the second portion is greater than a length of thescaffold; and wherein a length of the first portion is greater than alength of the second portion.
 16. The apparatus of claim 15, wherein theconstraining sheath slot is located distally of a distal end of thescaffold and a constraining portion of the constraining sheath appliesan inwardly directed radial pressure upon the scaffold to reduce recoilof the scaffold.
 17. The apparatus of claim 15, wherein the scaffold isplastically deformed by the balloon when the balloon is inflated, andwherein in use the scaffold recoils from the balloon by at most 5%, 10%or 20% when the sheath assembly is removed from the crimped scaffold.18. The apparatus of claim 17, the protecting sheath further comprisinga first and second end, each of the first and second ends having anouter diameter, the constraining sheath has an outer diameter that isless than the outer diameters of each of the first and second ends, andthe constraining sheath is between the first and second ends.
 19. Anapparatus, comprising: a catheter including a scaffold crimped to aballoon; and a sheath for the scaffold including a constraining sheathhaving a plurality of slots forming at least one strip not disposed overthe scaffold, wherein the constraining sheath comprises: a first portionnot disposed over the scaffold, a second portion disposed over thescaffold, a length of the second portion is greater than a length of thescaffold, and a length of the first portion is greater than a length ofthe second portion; wherein the at least one strip deflects outwardlywhen the constraining sheath is removed from the scaffold; wherein thescaffold undergoes plastic deformation when the balloon is inflated; andwherein the scaffold recoils from a crimped state by no more than 10%when the sheath assembly is removed from the crimped scaffold and beforethe balloon is inflated.